property has list_value and don't want to index will raise exception

[lucemia]

if a property is list_value and the property name is included in exclude_from_indexes
the following exception will raise.

The protobuf file has describe this behavior

// A list value.
  // Cannot contain another list value.
  // Cannot also have a meaning and indexing set.
  repeated Value list_value = 7;

https://github.com/GoogleCloudPlatform/google-cloud-datastore/blob/v1beta2-rev1-2.1.0/proto/datastore_v1.proto#L123

 File "/usr/local/lib/python2.7/dist-packages/gcloud/datastore/entity.py", line 244, in save
    exclude_from_indexes=self.exclude_from_indexes())
  File "/usr/local/lib/python2.7/dist-packages/gcloud/datastore/connection.py", line 425, in save_entity
    result = self.commit(dataset_id, mutation)
  File "/usr/local/lib/python2.7/dist-packages/gcloud/datastore/connection.py", line 329, in commit
    datastore_pb.CommitResponse)
  File "/usr/local/lib/python2.7/dist-packages/gcloud/datastore/connection.py", line 81, in _rpc
    data=request_pb.SerializeToString())
  File "/usr/local/lib/python2.7/dist-packages/gcloud/datastore/connection.py", line 59, in _request
    raise Exception('Request failed. Error was: %s' % content)
Exception: Request failed. Error was: A Value containing a list_value cannot specify indexed.

An example

entity = Dataset(dataset, kind, exclude_from_indexes=('a',))
entity['a'] = [1,2,3]
entity.save()

[dhermes]

/cc @pcostell

The error message seems strange since a is excluded. Though maybe it is referring to the property in general.

Also I'm curious why lists can't be indexed. IIRC a query like

class Foo(ndb.Model):
    bar = ndb.StringProperty(repeated=True)

q = Foo.query(Foo.bar == 10)

works just fine.

[pcostell]

Unlike Cloud Datastore, the App Engine datastore just uses repeated values as opposed to a list_value. I believe each value of 'a' should specify if it can be indexed or not, for example:

{  
  key: ...
  data: { 
    list_value {
      value {
        string_value: "hi",
        indexed: False
      },
      value {
         integer_value: 12,
         indexed: False
      }
    }
  }
}

[tseaver]

The protobuf spec says that items in a list_values "[c]annot also have a meaning and indexing set."

[pcostell]

I think the spec is actually saying that list_value cannot have a meaning and indexing set. The Value's inside can have indexing set. I'll be sure to tweak the protobuf spec to be more clear.

[tseaver]

I bow to your knowledge of the backend. Note that having the items in the list declare their indexing directly seems completely counter-intuitive to me.

[dhermes]

@pcostell ISTM we have a choice here to support a set of repeated values or a list_value. In our current implementation, the user doesn't select, we just imply list_value from the type of the value.

When and where would an end user decide if they wanted to use one or the other?

[pcostell]

@dhermes -- In Cloud Datastore list_value is the only option. Putting an entity with the same property multiple times will result in an error.

[dhermes]

@tseaver Did #399 fully fix this? ISTM it did, but want to double-check.

[tseaver]

Via #399.